1. Field of the Invention
This invention relates generally to the field of wells, particularly to the field of establishing branch wells from a parent hydrocarbon well. More particularly the invention relates to establishing multiple branch wells from a common depth point, called a node, deep in the well.
2. Description of the Related Art
Multiple wells have been drilled from a common location, particularly while drilling from an offshore platform where multiple wells must be drilled to cover the great expenses of offshore drilling. As illustrated in FIGS. 1A and 1B, such wells are drilled through a common conductor pipe, and each well includes surface casing liners, intermediate casing and parent casing as is well known in the field of offshore drilling of hydrocarbon wells. U.S. Pat. No. 5,458,199 describes apparatus and methods for drilling multiple wells from a common wellbore at or near the surface of the earth. U.S. Pat. No. 4,573,541 describes a downhole take-off assembly for a parent well which includes multiple take-off tubes which communicate with branched wells from a common point.
Branch wells are also known in the art of well drilling which branch from multiple points in the parent well as illustrated in FIG. 2. Branch wells are created from the parent well, but necessarily the parent well extends below the branching point of the primary well. As a result, the branching well is typically of a smaller diameter than that of the primary well which extends below the branching point. Furthermore, difficult sealing problems have faced the art for establishing communication between the branch well and the primary well.
For example, U.S. Pat. No. 5,388,648 describes methods relating to well juncture sealing with various sets of embodiments to accomplish such sealing. The disclosure of the  greater than 648 patent proposes solutions to several serious sealing problems which are encountered when establishing branches in a well. Such sealing problems relate to the requirement of ensuring the connectivity of the branch casing liner with the parent casing and to maintaining hydraulic isolation of the juncture under differential pressure.
A fundamental problem exists in establishing branch wells at a depth in a primary well in that apparatus for establishing such branch wells must be run on parent casing which must fit within intermediate casing of the well. Accordingly, any such apparatus for establishing branch wells must have an outer diameter which is essentially no greater than that of the parent casing. Furthermore, it is desirable that when branch wells are established, they have as large a diameter as possible. Still further, it is desirable that such branch wells be lined with casing which may be established and sealed with the branching equipment with conventional casing hangers.
An important object of this invention is to provide an apparatus and method by which multiple branches connect to a primary well at a single depth in the well where the branch wells are controlled and sealed with respect to the primary well with conventional liner-to-casing connections.
Another important object of this invention is to provide a multiple outlet branching sub having an outer diameter such that it may be run in a well to a deployment location via primary casing.
Another object of this invention is to provide a multiple outlet branching sub in which multiple outlets are fabricated in a retracted state and are expanded while downhole at a branching deployment location to produce maximum branch well diameters rounded to provide conventional liner-to-casing connections.
Another object of this invention is to provide apparatus for downhole expansion of retracted outlet members in order to direct each outlet into an arcuate path outwardly from the axis of the primary well and to expand the outlets into an essentially round shape such that after a branch well is drilled through an outlet, conventional liner-to-casing connections can be made to such outlet members.
These objects and other advantages and features are provided in a method and apparatus for establishing multiple branch wells from a parent well. A multiple branching sub is provided for deployment in a borehole by means of a parent casing through a parent well. The branching sub includes a branching chamber which has an open first end of cylindrical shape. The branching chamber has a second end to which branching outlet members are connected. The first end is connected to the parent well casing in a conventional manner, such as by threading, for deployment to a branching location in the parent well.
Multiple branching outlet members, each of which is integrally connected to the second end of the branching chamber, provide fluid communication with the branching chamber. Each of the outlet members is prefabricated such that such members are in a retracted position for insertion of the sub into and down through the parent well to a deployment location deep in the well. Each of the multiple outlets is substantially totally within an imaginary cylinder which is coaxial with and of substantially the same radius as the first end of the branching chamber. The prefabrication of the outlet members causes each outlet member to be transformed in cross-sectional shape from a round or circular shape to an oblong or other suitable shape such that its outer profile fits within the imaginary cylinder. The outer profile of each outlet member cooperates with the outer profiles of other outlet members to substantially fill the area of a cross-section of the imaginary cylinder. As a result, a substantially greater cross-sectional area of the multiple outlet members is achieved within a cross-section of the imaginary cylinder as compared with a corresponding number of tubular multiple outlet members of circular cross-section.
The multiple outlet members are constructed of a material which may be plastically deformed by cold forming. A forming tool is used, after the multiple branching sub is deployed in the parent well, to expand at least one of the multiple branching outlet members outwardly from the connection to the branching chamber. Preferably all of the outlet members are expanded simultaneously. Simultaneously with the outward expansion, the multiple outlets are expanded into a substantially circular radial cross-sectional shape along their axial extent.
After the multiple outlet members which branch from the branching chamber are expanded, each of the multiple branching outlets are plugged. Next, a borehole is drilled through a selected one of the multiple branching outlets. A substantially round liner is provided through the selected branching outlet and into the branch well. The liner of circular cross-section is sealed to the selected branching outlet circular cross-section by means of a conventional casing hanger. A borehole and liner is established for a plurality of the multiple branching outlets. A downhole manifold is installed in the branching chamber. Next multiple branch wells are completed. The production of each branch well to the parent well is controlled with the manifold.
The apparatus for expanding an outlet of the multiple branching sub includes an uphole power and control unit and a downhole operational unit. An electrical wireline connects the uphole power and control unit and the downhole operational unit. The wireline provides a physical connection for lowering the downhole operational unit to the branching sub and provides an electrical path for transmission of power and bidirectional control and status signals.
The downhole operational unit includes a forming mechanism arranged and designed for insertion in at least one retracted branching outlet member of the sub (and preferably into all of the outlet members at the same time) and for expanding the outlet member outwardly from its imaginary cylinder at deployment. Preferably each outlet member is expanded outwardly and expanded to a circular radial cross-section simultaneously. The downhole operational unit includes latching and orientation mechanisms which cooperate with corresponding mechanisms of the sub. Such cooperating mechanisms allow the forming mechanism to be radially oriented within the multiple branching sub so that it is aligned with a selected outlet of the sub and preferably with all of the outlets of the sub. The downhole operational unit includes a hydraulic pump and a head having hydraulic fluid lines connected to the hydraulic pump. The forming mechanism includes a hydraulically powered forming pad. A telescopic link between each forming pad and head provides pressurized hydraulic fluid to the forming pads as they move downwardly while expanding the outlet members.
According to a second, alternative embodiment of the invention, a branching sub is provided which allows multiple branches from a parent casing without the need for sealing joints and which allows the use of conventional well controlled liner packers and casing joints. The geometry of the housing of the branching sub allows the housing to achieve maximum pressure rating considering the size of the branch outlet with regard to the size of the parent casing.